1. Field of the Invention
The present invention relates to a gas sensor element and a gas sensor.
2. Description of the Related Art
An oxygen sensor having a pair of electrodes disposed on the outer surface of a solid electrolyte body and adapted to measure an air-fuel ratio of an internal combustion engine is known as a gas sensor for detecting a particular gas. Particularly, a laminate-type gas sensor in which two cells are laminated with a measuring chamber intervening therebetween (refer to, for example, Patent Documents 1 and 2 mentioned below) is known as a wide band gas sensor for detecting the concentration of oxygen contained in exhaust gas over a wide air-fuel ratio range of an internal combustion engine. In the laminate-type gas sensor, a first cell (also called an “oxygen concentration detection cell”) outputs a voltage corresponding to oxygen concentration in the measuring chamber to an external control circuit, and a second cell (also called an “oxygen pump cell”) pumps oxygen into/from the measuring chamber in accordance with current input from the control circuit.
As described in Patent Document 1, such a laminate-type gas sensor is usually driven by the control circuit, which feedback-controls current (hereinafter, also called “pump current”) to be input to the oxygen pump cell, based on the output voltage of the oxygen concentration detection cell. However, in some cases, the following problem can arise in the laminate-type gas sensor: the output voltage of the oxygen concentration detection cell fails to follow a change in the pump current of the oxygen pump cell and changes with a time lag. In the case of an excessive time lag, in some cases, the control circuit can oscillate, causing fluctuations in sensor output with a resultant difficulty in stable measurement and reduced measuring accuracy.
In order to cope with the above problem, according to the technique described in Patent Document 1, the control circuit employs a high pass filter which uses a resistor and a capacitor. This configuration restrains oscillation of the control circuit as well as fluctuations in sensor output, which could otherwise result from the oxygen concentration detection cell output being greatly affected by a change in the pump current of the oxygen pump cell.
Patent Document 2 discloses a technique for restraining oscillation of the control circuit by providing a leakage section formed of zirconia between the oxygen concentration detection cell and the oxygen pump cell.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2002-243700
[Patent Document 2] Japanese Patent Application Laid-Open (kokai) No. 2013-50440
3. Problem to be Solved by the Invention
However, sufficient studies have not be conducted on the position and size of the leakage section, leaving room for improving the position and size of the leakage section for effectively restraining oscillation of the control circuit.